


Swapped Out

by Anubisisbunagirl



Category: Undertale (Video Game)
Genre: Other, Underswap Papyrus (Undertale), Underswap Sans (Undertale), swapped
Language: English
Status: In-Progress
Published: 2019-10-07
Updated: 2020-05-14
Packaged: 2020-11-27 00:22:20
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,978
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20939219
Author URL: https://archiveofourown.org/users/Anubisisbunagirl/pseuds/Anubisisbunagirl
Summary: Sans wasn't sure what to think of this new weird place, he wasn't sure what to think of this new weird Papyrus. He only knew once thing for sure, he was in the wrong universe and if he didn't find a way out soon, he would be stuck there forever.





	1. Ya boi is in the zone

15 hours. 15 to go.

Sans laid down in his chair, stretching his legs out to rest on the table. Perfect. Diagnostic testing was almost done. Then he wouldn’t have to worry about that mess for another few runs. Sans groaned and rubbed his head, he wished this headache would do away.

He couldn’t wait to go back to being lazy again, he always despised doing work. Testing wasn’t hard per say, it was just tedious, and Sans HATED tedious.

Sans chucked, if only he had the work ethic of Papyrus. Sometimes Sans thinks his brother absorbed all their fathers work ethic. Gaster was quite the workaholic.

Sans paused. He hadn’t thought of Gaster in quite some time. Gaster…. The one stuck in the void. The one Sans… the one Sans trapped in the void. If only he could see Sans now. Stuck in the terrible time loop.

He would laugh and brag that he would have been able to find a way out. Maybe if Sans hadn’t trapped him……

Sans clenched his fists.

Maybe if Sans hadn’t trapped Gaster Papyrus wouldn’t be trapped in the time loop. Sans wouldn’t have cared as much if he was trapped alone, that was his fault.

But Papyrus? Poor Papyrus didn’t even know what happened to their father. He didn’t even know that he had a father. And it was all thanks to Sans. Sure Gaster was a dick, but Papyrus deserved a father.

Sans sighed, bringing his feet down and hugging his knees. He felt like shit. He gazed sadly at the glowing machine, checking the monitor. Everything seemed stable so far. Boy, those graphs were boring to look at. Sans wished he could just get up and leave it until it was over, unfortunately he did need to watch to make sure it was stable.

“SANS? SANS? WHERE ARE YOU LAZY BONES?”

Sans jolted up, accidently knocking over his nearby beer bottle. The liquid splashed outwards, sizzling against the machine as it made contact. Sans whirled around to look at the machine in horror.

BEEP  
BEEP  
BEEP BEEP

The monitor began to beep as the graph began to skyrocket.

BEEP BEEEP BEEP

Sans ran to the monitor, desperately typing at it, trying to fix his mistake. But the beeping only grew louder and higher.

BEEP BEEP BEEP BEEP

BEEP BEEP BEEP BEEP BEEP

Sans desperately mashed the keys, trying to stop the loud beeping. As the beeping grew and grew, Sans fell to the floor closing his eyes and bracing for impact

And then…

Silence.

Sans peeked through his hands cautiously. Looking at the Machine it looked different. The graph was completely off, in fact all of his monitoring probes seemed to have vanished. Sans peered curiously at the machine. It seemed to be completely off besides a small screen. The screen read 14 H 37 M 28 S. Sans cocked his head, this was weird. What was he gonna-

Papyrus!

Wasn’t Papyrus outside?!

Sans quickly pulled off his lab coat, bolting to the door and pushing it open. He let out an icy breath as he adjusted to the cold outdoors. Looking around he didn’t see Papyrus.

“pap?” He called into the howling wind taking a few steps into the snow.

He hurried forward calling for his brother and fighting through the snow. After a while trudging through the snow, he finally noticed a tall lanky figure standing in a clearing. Breathing out a sigh of relief Sans approached his brother.

“papyrus” he reached out to his brother before stopping cold.

The figure turned around to reveal… Papyrus? He had the same face and figure anyway, but he seemed… different. His expression was really laid back and lazy, he had his hands in the pockets of a long orange sweater. Not to mention the smoking cigarette in his mouth.

Slim took in Sans standing in front of him. He raised his eyebrows in surprise and cocked his head.

“p-papyrus? is that you?” Sans asked, confused.

Slim chewed thoughtfully on his cigarette before beginning to open his mouth, however he didn’t get very far as a voice sounded through the snow.

“Sans!”

Sans whirled around to find Alphys. But… but not? She wore a tank top and has a large claw mark running on her left eye. The shivering Alphys quickly made her way over to sans, grinning tooth fully.

“There ya are, you squirt.” She reached over and grabbed Sans, rubbing his head aggressively.

Sans grunted in surprise before ducking out of her grip. She gave him a long look of confusion, taking in his appearance.

“Whoa. What happened to you Sans? You look like shit. And what the hell are you wearing?”

“uhhh…” Sans looked desperately to Slim who gazed back at him. Slim took out with cigarette to puff a large plume of smoke before giving Alphys a lazy grin.

“Awww Alphys, You Know My Bro. You’ve Been Working Him Down To The BONE.” Slim shrugged easily.

A pun? That confused Sans, Papyrus making puns wasn’t exactly odd, but he normally didn’t do them without being provoked by Sans.

That did it. Sans could say for sure that whoever that skeleton was, it certainly wasn’t his brother. He was acting like… like… like Sans!

Slim cleared his throat, “As For The Case Of His Clothing, His Normal Battle Armor Is In The Wash, So I Lent Him A Hoodie. You Know Sans, He Has LOADS Of Fun Doing The Laundry.” Slim gave Sans a pointed look.

Ok. That made sense. If Papyrus was acting like him, Sans should act like Papyrus.

Sans groaned “brother. that wasn’t even a good pun!” Sans mentally catalogued the pun to use later when he got home.

Slim grinned in relief turning back to Alphys, “Heh. Never Gets Old.”

Alphys rolled her eyes before turning back to Sans, “Anyways squirt, the reason I came here was to let you know that todays lesson is off. Undyne wanted to use me as a test subject for her latest strength test, and you know me. Always down to show everyone just how strong I am.”

She held up her arm, flexing. Sans couldn’t help but gawk, he didn’t know Alphys could be this jacked. If he and Pap were switched, he guessed that Undyne and Alphys must be too. It was just so bizarre to see the bookworm and nervous Alphys to acting so strong and confident.

Alphys rubbed her shoulders, “Well it’s best I take my leave now, unfortunately Snowdin weather does not agree with me. We’ll have to cook tacos another time, ‘k?”

Sans nodded slightly offering a wide smile. This seemed to satisfy Alphys as she turned and trudged back through the snow and out of sight.

Sans let his mouth relax into something of a frown as he turned back to Slim. Slim stared back with a masked expression for a few seconds, before abruptly walking past Sans back towards the house.

“hey!” Sans called after Slim, running after the tall Skeleton.

Slim made no signs as to whether he noticed Sans and continued walking until he reached the house, making a sudden turn towards the secret lab. Sans watched in fascination as Slim easily opened the doors and walked inside, leaving the door slightly ajar for Sans.

Sans pushed his way into the lab, glancing around more carefully than the first time he was there. The lab looked so similar to his own, but different in a few variations. A picture caught Sans eye as he passed through the room, it appeared to be one of Slim and Blue. He picked it up, dusting off a light coat of grime and staring, transfixed at his alternate self.

Blue looked so young, so vibrant. He was standing on his tiptoes trying to put an arm around Slims shoulder as he smiled wide for the camera. Slim held out a halfhearted wave with one hand, and the other remained in his pocket as he grinned lazily at the camera, though his eyes only sought Blue. He seemed tired, careless, and older than he should have looked.

Sans could feel his body shiver at this form of Papyrus. It was wrong. Papyrus should always be happy and smiling, he shouldn’t have looked so… so tired. But if Sans and Paps were switched in this universe, didn’t that make Slim just like himself. Weren’t they basically the same. Then would Paps be Blue? Thinking about it gave Sans a headache so he decided to put the picture down and walk away.

Sans stopd right behind Slim, who was facing the machine silently.

“hey pa-“

“You’re Not My Brother, Are You?”

Sans paused, wringing his hands, “no. i’m not.”

Slime chuckled a bit, turning towards Sans, his eye lights had gone out. He puffed out a ring of smoke before holding the cigarette between his fingers, glaring at Sans.

“Then Where Is He?”

“you shouldn’t smoke paps, it’s bad for you.”

Slim scoffed, “People In Glass Houses, Shouldn’t Throw Stones.”

“i don’t smoke!” Sans exclaimed, offended.

“You Don’t Smoke, I Don’t Drink… Same Difference.” Slim shrugged.

Sans felt a blush appear on his cheeks as he turned away.

“Now,” Sans could smell the smoke heavy in the air as Slim knelt down next to him, “I Ask Again, Where Is My Brother?”

Sans turned to look Slim directly in the eyes, “i don’t know.” He said in a level voice.

Slim searched his face for a while before standing up, “Stay here.” He commanded, “I Need To Check Something.” The world seemed to pause for two seconds until Slim was suddenly gone.

“tch, teleporting bastard.”

Sans approached the machine thoughtfully, glancing down at the numbers he saw a new sequence displayed. 14 H 08 M 13 S. It had changed. Almost like a… a countdown? Sans had a sudden flash to right before the machine had gone off. 15 hours, 15 hours until the diagnostics were complete. Now 14 hours 8 minutes and 4 seconds apparently.

But what did it mean now? What would happen when the machine reached 0? Sans wasn’t sure he wanted to find out. But he knew that his appearance in this… alternate universe had to have something to do with the machine. Maybe when the timer ran out, Sans was stuck here.

Sans nervously tapped his bones against the machine, being stuck in this universe sounded awful. He would never get to see Paps again. HIS Paps. Sans wasn’t sure what he would do without Papyrus’s smiling face and excited attitude, he would probably waste away into nothingness.

“He Is Gone…”

Sans jumped back, startled, as Slim appeared next to him. Slim looked utterly pissed as he stared at Sans, “Looks Like You Got Some Explaining To Do Here, Bud.”

Sans nodded nervously, “i think it has something to do with the machine. i was working on it when it began to malfunction. next thing i knew, i was here, in some kind of alternate universe, where everything is… swapped or something. ”

Slim pondered this for a few seconds, chewing on his cigar thoughtfully, “And When You Got To This Universe, It Couldn’t Handle Two Sans, So It Must Have Sent My Sans To Your World.”

Sans jolted, the other Sans? In His universe? “with papyrus?”

Slim grinned, “I Should Have Realized. Of Course, There Is Another Me. Don’t Worry, My Sans Is Harmless. Papyrus Will Be Fine.”

“i don’t doubt it.” Sans grinned. But man, Papyrus was gonna be hella confused if Sans were to start acting more like him.

“So. How Do We Send You Back?” Slim asked.

“what, eager to get rid of me so soon?” Sans grinned, “well. it’ll be snow easy task.”

Slim chuckled, “Heh, I Will Admit, It’s Nice To Have Someone Here Who Appreciates Puns Like I Do.”

Sans snickered slightly, if only Paps were here, he would die to know that there was another version of himself being lazy and telling puns.

Sans sighed, looking to the machine sadly, he sure hoped Paps was doing ok.


	2. When two balls of pure happiness meet.

**Summary for the Chapter:**

> Papyrus finds himself with a strange brother look alike, and it'd appear his real brother might be in trouble.

**Notes for the Chapter:**

> I like to think that Papyrus knows about the resets and Gaster even if Sans tries to hide it. I also just wanna see pap bond with blue because they are sweet bois! : 3

Papyrus couldn’t help but feel a little let down. His morning had started off so well, Sans had even gotten out of bed after only two times of Papyrus provoking him. Sans had eaten all his breakfast spaghetti (a new record) and seemed a bit more chipper than he normally did. Perhaps it was foolish, but Papyrus genuinely had hope that maybe Sans wouldn’t slack off or go to Grillby’s instead of watching his station.

Unfortunately, it seemed his hope really was foolish. Papyrus sighed as he aporached Sans’ empty post, at least Sans normally had the decency to stick around before lunch. Seemed like his chipper attitude in the morning wasn’t any excitement for his job.

Papyrus huffed slightly, he was trying so hard to get Sans to care more and be more excited, but Sans had an unparallel amount of laziness.

That did it.

Papyrus was going to find Sans and get him to do a full shift for once in his life, even if it took all of Papyrus’ lunch break. With a determined expression, Papyrus marched his way through the snow and back into Snowdin. He made a brief stop at Grillby’s, no sign of the skeleton. Well, at least he wasn’t drowning himself in Ketchup so early.

Papyrus made his way to their house, muttering under his breath about the sheer laziness of his brother. However, it seemed that Sans wasn’t at their house either. That was odd. Papyrus cocked his head in confusion at the sight of his brothers’ empty room. Strange indeed…

“SANS?” He called, his voice echoing through the empty house.

He made his way down the stairs, still calling for Sans, and still receiving no response. He made his way outside still calling.

“SANS? SANS? WHERE ARE YOU LAZY BONES?”

But all he heard was the howling wind. It seemed Sans was nowhere near the house. Papyrus was growing increasingly concerned, there were only so many places his brother liked to go. Certainly not into Waterfall… maybe… the ruins? Papyrus knew he often went there, he had no clue why but it was worth a try.

But just as Papyrus turned around to head towards the ruins, he could make out a faint beeping sound. Papyrus turned back towards the house, the sound seemed to be growing louder and louder.

“S-SANS?” Papyrus called, sprinting back towards the house. A sudden flash appeared from the back side of the house. Papyrus felt his body grow cold; it came from the lab. The secret-not-so-secret lab that he knew Sans was very protective of.

Papyrus quickly rushed towards the lab, hoping that Sans wasn’t doing anything weird or dangerous. “SANS? WAS THAT YOU?” He called, reaching the door.

He swung the door open, “YOU OK?”

The entire lab was in disrepair, it seemed like the bulb had cracked, making it hard to see. But papyrus could make out papers scattered all over the floor. He squinted into the darkness, “ARE YOU THERE, BROTHER?”

A slight coughing sound came from inside the lab, and Papyrus wasted no time rushing over. He could see the small form of Sans sprawled across the floor and Papyrus quickly put his hand on his brothers’ shoulder to help him up. Blue slowly stood up with the help of Papyrus, and Papyrus led them both out of the lab and into the sun.

As soon as they were out, Papyrus looked over to Sans and opened his mouth. But… that wasn’t Sans before him. He took a small step back in shock as he took in the skeleton’s appearance. He looked like Sans for sure, small and round, but he wasn’t dressed like Sans would dress. He was wearing a small bandana around his neck, a t-shirt with some sort of shoulder pads, and blue gloves. He also seemed to have both of his eye lights working, bright and blue unlike the small white pinpricks Sans would have.

Papyrus cleared his throat slightly, “PARDON ME, BUT WHO EXACTLY ARE YOU?”

“Myeh?” The small skeleton looked up the tall skeleton before him, Blue seemed just as confused as Papyrus did. “A better question is who are you? And why did you bring me into that dark room?”

Papyrus looked offended, “I DID NO SUCH THING, I JUST FOUND YOU THERE. BESIDES, I ASKED YOUR NAME FIRST.”

The small skeleton straightened up and put on a dazzling smile. “I am the Magnificent Sans!”

Papyrus couldn’t help but let out a small chuckle, the ‘Magnificent Sans’ had such a high energy aura around him. But then Blue’s words hit him, ‘Sans’? Huh. What were the chances his brother had a lookalike with the same name? Papyrus narrowed his eyes, what were the chances indeed…

“And your name?” Blue called, pulling Papyrus back into the moment.

Papyrus cleared his throat and struck a heroic pose, “I AM THE GREAT PAPYRUS!” He honestly felt pretty cool as his cape blew in the wind.

Blue cocked his head slightly, “That’s funny. I have a brother with the same name and looks as you. Though I am sure he wouldn’t be caught dead calling himself ‘great’.”

“WELL, I ALSO HAVE A BROTHER SIMILAR TO YOU. THOUGH I DOUBT HE’D CALL HIMSELF MAGNIFICENT.”

The two skeletons gazed at each other for a while, neither sure what to do with the other. At last, Papyrus cleared his throat. “MAYBE YOU SHOULD COME INSIDE. I CAN COOK US BOTH A PLATE OF SPAGHETTI AND YOU CAN TELL ME HOW EXACTLY YOU GOT IN MY BROTHERS LAB.”

Blue gave a slight nod and followed Papyrus into the Skele-bros house.

Blue walked through the house, taking in everything about it while Papyrus began cooking up some Spaghetti. Blue seemed really fascinated by everything in the house, chuckling slightly at the discarded sock on the ground. At last the two skeletons sat down together.

They awkwardly picked at their spaghetti, avoiding eye contact for a little before Blue spoke.

“I don’t think this is anything normal. I mean, you are almost an exact replica of my brother and it seems your house is eerily similar to mine, though everything is slightly off.”

Papyrus nodded, “IT WOULD APEAR THERE IS SOMETHING MORE THAT MEETS THE EYE GOING ON. HOW EXACTLY DID YOU GET INTO MY BROTHERS LAB?”

Blue shrugged, “I don’t know. I was patrolling the woods near Snowdin when I suddenly felt a tug at my soul.” He absentmindedly touched his chest as if remembering the feeling. Judging by his expression, it wasn’t a pleasant feeling. “Everything went white and the next thing I knew I was on the cold stone ground and you were there.”

Papyrus considered this for a little before rubbing his hand on his skull, “WOWIE. THAT IS VERY ODD INDEED. IF I WERE TO GUESS, I’D SAY SANS WAS PROBABLY DOING SOMETHING IN HIS LAB THAT MAY HAVE WENT WRONG.”

Blue nodded his agreement, polishing off the last of his Spaghetti. Papyrus grinned, “ENJOY THE SPAGHETTI?”

Blue smiled, his eyes shining, “It was MAGNIFICENT! Meyehehe. I will have to cook you some Tacos sometime!”

Papyrus grinned back; it was like he found his long-lost twin. The two were more alike than they appeared. It was so odd seeing Sans smile so wide and happy, but as cool as Blue was Papyrus deeply missed Sans. His Sans. As lazy and closed off as that Sans was, he was the one who had been with Papyrus and practically raised him after… after their father…

“So, to the lab?!” Blue exclaimed, standing up.

Papyrus jolted out of his thoughts and gave Blue an affirmative nod. “YUP, LETS FIGURE OUT WHAT HAPPENED, SHALL WE?”

The pair trudged back out into the snow and to the lab. They made sure to bring a nice lamp since the lights were broken in there. As soon as they entered, Papyrus set to work sifting through the papers on the floor trying to find a clue while Blue examined the lab.

Most of the papers were just equations and weird notes in a weird language that Papyrus didn’t understand. He came across a few notes that were a little odd, accounting something about ‘resets. Papyrus looked over those notes sadly, despite what Sans thought, he wasn’t oblivious to the resets. He just ignored them completely and lived every day like it was a new day.

Sans didn’t need to know that he remembered the resets through dreams, it would probably send him into a deep despair and Papyrus wasn’t ready to see his brother give up completely. Papyrus’ biggest asset was bringing Sans hope by being oblivious. So if that’s what it takes, that was what Papyrus was gonna do. 

Papyrus could feel Blue behind him, staring at the notes. Papyrus turned to face him, and judging from his expression, he knew what the ‘reset’ meant too. The pair shared a knowing look, and an unspoken thing came between them. They wouldn’t discuss the resets. Neither of them were to acknowledge it was even there.

Papyrus carefully placed the notes about the resets in a nearby drawer before turning towards the machine. It seemed to be the center of the anomaly, where Blue had come through and probably where Sans had gone through too. Papyrus went up to examine the machine, it was buzzing faintly. Papyrus turned his attention to the monitor where a graph was displayed. It seemed the graph had a sudden spike and was slowly going back down to a stable condition. That was odd.

“Hey, what’s this?” Blue asked, pointing to some sort of timer.

Papyrus examined the timer, it read “14 H 7 M 34 S”. He frowned, “A COUNTDOWN?”

Blue watched the seconds ticking down, “And what happens when it reaches zero?”

“NOTHING GOOD… IT SEEMS SANS DISAPEARENCE HAS SOMETHING TO DO WITH THIS MACHINE. AND YOU CAME THROUGH AT THE SAME TIME…. I THINK I READ SOMETHING IN SANS’ NOTES… SOMETHING ABOUT ALTERNATE UNIVERSES?”

Blue nodded slowly, “That’d explain why everything in this dimension is so backwards. So your Sans is probably in my dimension.”

Papyrus looked over worriedly. Blue gave him a small smile, “Don’t worry, I’m sure my Papyrus will take care of him. He may be a little gruff but he cares about people.”

Papyrus nodded, reassured. “BUT HOW ARE WE GONNA GET YOU BACK INTO YOUR DIMENSION AND MY SANS BACK INTO THIS DIMENSION?”

Blue looked to the machine thoughtfully, “If I came in through this thing, I think we will need to get back through that thing. Do you know how to operate it?”

Papyrus shook his head, “SANS IS INTO THE SCIENCE-Y STUFF. I DON’T KNOW ANYTHING ABOUT THIS MACHINE OR WHAT IT’S MEANT TO DO.”

Blue nodded slowly, “Yeah, if anything I’d say my Papyrus and your Sans are the most qualified to do anything…”

The two sat in silence for a little, both feeling a little useless.

“SO, ARE WE GONNA WAIT FOR THEM TO FIGURE IT OUT?”

Blue thought for a few seconds before grinning, “No. We are gonna find a way to fix this. We may not be the best at machines and science stuff, but we are great at puzzles. And it seems like this is just a big puzzle waiting to be solved.”

Papyrus felt his face break into a grin as well, “WE MAY BE UNDERESTIMATED MOST OF THE TIME, BUT I KNOW WE CAN FIGURE THIS OUT TOGETHER. FOR OUR BORTHERS.”

The two shared a look of determination and pride, they were going to figure this out together.

As Blue began to sift through the papers again, Papyrus sat down and examined the probes and monitors Sans had set up.

“HOLD ON SANS… WE’RE ON OUR WAY.” He smiled. 

**Notes for the Chapter:**

> Yeehaw one chapter lefttttt  
Also I didn't revise this chapter so it's all raw  
Sorrry

**Author's Note:**

> Here is my raw unedited work that I made in math class, enjoy!


End file.
